Machine vision or inspection systems have become a vital component in integrated manufacturing systems. They can sort, package, and perform defect analysis without human intervention. For instance, by inspecting holes being drilled the system can determine if a drill bit is worn. However, most machine vision systems are based upon digital electronic technology that uses serial or one dimensional processing. For instance, an image is captured and stored as a matrix of electrical signals. The image is then preprocessed to enhance edges, improve contrast, and otherwise isolate the object to be recognized. A comparison function compares the enhanced image to one or more stored reference images. These functions are typically performed by standard microelectronic, digital equipment on a bit-by-bit or vector basis. Accordingly, the techniques are typically serial and inherently one dimensional, whereas the images being processed are two dimensional. This dichotomy results in very intensive processing requirements, is particularly difficult for one dimensional digital equipment, and takes a relatively long time to complete. Digital processing hardware has been enhanced and the software and algorithms have been improved to provide some improvements in prior art machine vision systems. However, these improvements have come at the expense of additional system complexity, system costs and programming complexity.
In some systems, the image to be processed is converted into a Fourier domain. The Fourier transform maps all of the information about the image of the object into a very useful, symmetrical pattern which represents the object in terms of its spatial frequencies. However, the calculation of a Fourier transform on a digital computer is extremely intense, and may take a computer as powerful as a Micro Vax II about a minute to complete. Even powerful and expensive state of the art array processors take a full second to merely produce the transform. In modern industrial plants, the production line rates are often a full order of magnitude faster than this.
Accordingly, it is an object of the present invention to provide an optical processing system.
It is a further object of the present invention to provide an optical processing system that can rapidly provide an electrical signal representing the Fourier transform of an image of an object.
It is a still further object of the invention to provide an optical processing system that utilizes a Fourier transform of the image being processed to produce an electric output signal characteristic of any differences between the image being processed and a reference image.
It is a still further object of the present invention to provide an improved spatial light modulator to impress the image of the object being processed onto a coherent light beam.
These and other objects, which will become apparent from this application, are accomplished by the Fourier transform optical processing system of the present invention. The method and apparatus of the present invention include generating an electrical signal in response to a first image and modulating a beam of coherent light with means that is responsive to the electrical signal. A Fourier transform image of the modulated coherent light beam is formed, an then detected. The detector provides a second electrical signal representative of the Fourier transformed image. Other aspects of the invention include comparing the second electrical signal to a reference electrical signal for producing an output signal representing any differences; optically preprocessing the image; detecting the Fourier transform image and generating signals representative of its Fourier transform characteristics; and modulating a coherent light beam using a liquid crystal or other spatial light modulating device.